The so-called switching structure, in the application of telecommunications, is a kind of network equipment which achieves routing for data units and forwards them to the node of next hop.
When the distribution of arriving traffics to a switching system is unbalanced, some ports or internal line will become saturation while others are still in idle state because the internal capacity of any switching system is bounded. In order to avoid unbalanced traffic, load-balancing switching structure is used to solve this problem. The structure makes traffic uniformly distributed inside the switch, that is, the utilization of all ports and internal lines are identical. Such switching structure can improve throughput to the maximum extent and decrease the internal blocking.
The structure of load-balancing Birkhoff-von Neumann (LB-BvN) switches can solve the problem of internal blocking.
As shown in FIG. 1, the LB-BvN switch consists of two crossbar switch stages and one set of virtual output queue (VOQ) between these stages. The first stage performs load balancing and the second stage performs switching. This switch does not need any schedulers since the connection patterns of the two switch stages are deterministic and are repeated periodically. The connection patterns should be selected so that in every consecutive N time slot, each input should connect to each output exactly once with a duration of one time slot. It is clear this said load-balancing switching structure solves the problem of data blocking.
However, traffic is different and un-uniform for each input port, the number of packets belong to different flows is variable, so the size of mid-stage VOQ is also different. As queues are served uniformly independent of their sizes, this LB-BvN structure brings about queuing delay and packet out-of-sequence problem. Packet out-of-sequence makes TCP (Transmission Control Protocol) triggering a fast recovery processing, and its sliding window is reduced by half, thus the end-to-end throughput of this connection is reduced by half.